Pars intermedia

The pars intermedia is a part of the pituitary gland, which is an important endocrine organ located at the base of the brain. The pituitary gland is divided into three distinct parts: the anterior pituitary (adenohypophysis), the posterior pituitary (neurohypophysis), and the pars intermedia. The pars intermedia is situated between the anterior and posterior lobes of the pituitary gland.

Structure

The pars intermedia is a thin layer of cells that is often considered part of the anterior pituitary. It is composed of basophilic cells and is less developed in humans compared to other species. In some animals, such as fish and amphibians, the pars intermedia is more prominent and plays a significant role in physiological processes.

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Diagram of the human pituitary gland showing the pars intermedia.

Function

The primary function of the pars intermedia is the production of melanocyte-stimulating hormone (MSH), which is involved in the regulation of skin pigmentation. MSH stimulates the production and release of melanin by melanocytes in the skin and hair. In humans, the role of MSH is less pronounced, but it is still involved in the regulation of appetite and energy homeostasis.

Development

During embryonic development, the pituitary gland forms from two distinct ectodermal tissues: the Rathke's pouch and the infundibulum. The pars intermedia originates from Rathke's pouch, which also gives rise to the anterior pituitary. As development progresses, the pars intermedia becomes a thin layer of cells sandwiched between the anterior and posterior lobes.

Clinical Significance

In humans, disorders of the pars intermedia are rare. However, in some animals, such as horses, dysfunction of the pars intermedia can lead to conditions like Equine Cushing's disease, also known as pituitary pars intermedia dysfunction (PPID). This condition is characterized by an overproduction of hormones, leading to symptoms such as increased coat length, weight loss, and laminitis.

Related pages

• Pituitary gland
• Anterior pituitary
• Posterior pituitary
• Melanocyte-stimulating hormone
• Endocrine system